Bearing assembly

ABSTRACT

A bearing assembly is disclosed which addresses the problem of axially retaining a bearing journaled onto a shaft within a casing in an axially compact and technically economic and reliable way by first mounting a retaining plate ( 6 ) onto an outer race of the bearing ( 1 ). The mounting can be achieved by press fitting onto a shoulder so that the retaining plate can rotate relative to the outer race. The bearing is then journaled onto a shaft ( 4 ) and inserted into a compact casing ( 3 ) so that the outer race is guided into a housing ( 2 ) formed in an end wall of the casing ( 3 ). The retaining plate can then be rotated as required to align fastening bosses ( 7 ) with holes ( 8 ) to be engaged by screws ( 9 ) so that the retaining plate us urged axially against the outer race.

PRIORITY INFORMATION

This application is a divisional of U.S. Patent Application Ser. No.11/367,215, filed on Mar. 2, 2006, which claims benefit of InternationalPatent Application No. PCT/GB2004/003778, filed on Sep. 3, 2004 andclaims priority to Great Britain Patent Application No. 0320650.5, filedon Sep. 2, 2003, all of which are incorporated by reference in theirentirety.

BACKGROUND OF THE INVENTION

The present invention is concerned with the form of and a method offorming a bearing assembly particularly adapted for use where thebearing is subject to axial loads, in very compact machine assemblieswithout fastening tool access to the bearing housing and where robotmachine assembly is desirable.

The present invention arose in addressing the problem of assembling abearing into compact vehicular gear box housing where the bearing isjournaled onto a gear shaft of the gear box together with a number ofother components such as gears. It will hereafter be described in thatcontext but unless otherwise stated the invention may have applicationsin many other similar structures. In such a gear box the gear shaft isjournaled onto a bearing and the bearing received into a bearing housingformed in the gear box casing. The fitting of the outer is typically anengineering interference fit or similar means of location such that theouter is not free to take up a different angular orientation. Inoperation the shaft is subject to axial forces which urge the bearingout of its housing in each axial direction. The forces directed axiallyout of the casing are resisted by a shoulder formed in the casing.However a retaining means must act between the outer race of the bearingand the casing to prevent axial displacement in the opposite direction.An example of conventional means may be a circlip received into a grooveformed in the wall of the bearing housing. However, the installation ofsuch retaining means requires access by a tool to the inside of thecasing and is difficult to implement robotically. Further the use ofcirclips and like devices requires a loose fit between the bearing outerand the circlip which undesirably permits axial movement of the bearingand occupies space in the axial direction. Also, circlips and similardevices are not easy to disassemble without good tool access. If suchaccess requirement can be obviated robot assembly will be possible andthe bulk of the gear box can be reduced with numerous advantages whichwill be apparent to the skilled person.

Also known in the prior art is EP1265339 which discloses a bearingassembly in a motor. A retaining plate is first mounted temporarily ontoa shaft. A bearing is then journaled onto the shaft. The assembledretaining plate and bearing are then inserted into the motor casing withthe outer race of the bearing being inserted into a bearing housing.This presents a problem in that the retaining plate must be dismountedfrom the shaft before operation. Further the retaining plate cannot bearranged to sit flush with the inner end of the bearing so that theaxial length of the bearing and housing assembly is not minimized.

SUMMARY OF THE INVENTION

Accordingly to alleviate these problems the present invention provides abearing assembly comprising:

a bearing assembly comprising: a bearing having an outer race forreception in a bearing housing formed in a casing and an inner race tobe journaled onto a shaft, and a retaining plate mounted onto the outerrace before assembly into the bearing housing or onto the shaft andprovided with fastening means to cooperate with fastening means providedin or on a wall of the casing opposing the retaining plate.

The retaining plate may be irrotatably fastened for some applications,for example by press fitting. However, in the preferred embodiment ofthe invention the retaining plate is fastened so as to rotate withrespect to the outer race thus providing for convenient alignment of thefastening means after the outer race is irrotatably retained in thehousing.

Further according to the present invention there is provided a method offorming a bearing assembly comprising the steps of:

mounting a retaining plate on an outer race of a bearing whereby whenthe bearing is seated in a bearing housing it is axially retained by theretaining plate which is secured by fastening means acting between acasing in which the bearing housing is formed and the retaining plate.

According to another aspect of the present invention there is provided amethod of forming a boss in a plate to be subject to cyclic fatigueloads in use comprising, selecting the material of the plate to have ahigh strain hardening coefficient in excess of 0.35, and press formingthe boss against a die such that the radius of curvature of the regionbetween the original plate and the wall of the boss complies with theformula:radius=plate thickness X Awhere “A” has a value between 0.3 and 0.7 such that the arcuate portionof the boss work hardens under load to produce a region having a highlocal tensile strength.

BRIEF DESCRIPTION OF THE DRAWINGS

The bearing assembly of the present invention alleviates the problemsdiscussed above as will be apparent from the following non limitingdetailed description of one embodiment of the bearing assembly andmethod of forming a bearing assembly which refers to the figuresdescribed briefly as follows:

FIG. 1 is a sectional elevation through a gear box casing showing thebearing assembly during installation in a bearing housing formed in thecasing,

FIG. 2 is an enlarged sectional elevation through a die punch showingthe formation of a clinching lip (17) on a retaining plate of theassembly,

FIG. 3 is an enlarged sectional view through a shoulder of a bearing asthe retaining plate is mounted on it,

FIG. 4 is an enlarged sectional view showing the engagement of theclinching lip (17) with the groove in the retaining plate,

FIG. 5 is a sectional view through the retaining plate alone and,

FIG. 6 is a plan view of the retaining plate.

FIGS. 7A and 7B show the formation of a boss in the retaining plate.

DESCRIPTION OF THE INVENTION

Referring to the drawings, FIG. 1 shows a bearing assembly comprising, abearing 1 having an outer race for reception in a bearing housing 2formed in a casing 3 for a vehicular gear box. The inner race of thebearing 1 is journaled onto a shaft 4. The bearing 1 is to be receivedinto the bearing housing 2 so that it abuts a shoulder 5 formed in thehousing to prevent displacement of the bearing in the axial direction(with respect to the shaft) out of the casing 3. To prevent the bearing1 being displaced in the opposite axial direction a retaining plate 6 ismounted for rotation with respect to the outer race of the bearing 1.When the bearing 1 is seated in the housing fastening means provided bythreaded bosses 7, formed in the retaining plate 6, are aligned withthrough holes 8 formed through the casing 3 so that screws 9 can bedriven through the holes to engage in the bosses 7 and retain theretaining plate 6. The bearing assembly can therefore be installed wherethe components are mounted on the shaft in such close proximity to theretaining plate as to prevent the operation of the tools between theretaining plate and the components and where the casing surrounds thebearing shaft, components and retaining plate to the extent that afastening tool cannot operate on the retaining plate. This in turnallows further components such as gears 10 to be assembled on to theshaft in very close proximity to the bearing 1 before the bearingassembly and shaft is installed.

The retaining plate 6 is folioed from metal strip by first punching outthe bosses 7. A centre hole 11 is then punched out. A plurality ofclinching lip 17 s 12 are then formed along arcs spaced around thecircular inside edge of the retaining plate 6. In the present examplethree lip 17 s are formed, however, according to specific requirementstwo to five lip 17 s may be formed.

FIG. 2 shows the use of a specially designed punch tool to form theclinching lip 17. The hole 11 is located on a die plate 13 surrounding acircular guide 14. A platen ring 15 is then pressed against the exposedsurface of the plate before a coining punch 16 is driven part way intothe surface of the retaining plate spaced a small distance from the edgeof the hole. The coining punch has a wedge shaped blade 27 which engagesin the surface of the retaining plate to plastically deform the edge ofthe plate so forming a lip 17 on the edge which projects up, i.e. in theaxial direction, from the surface of the retaining plate and leaves agroove 18 along its edge remote from the hole. The coining punch mayalso form notches 19 at each end of the arc to control the deformationat each end. Each arc deformed by the coining punch extends over between12 and 36 degrees of arc so that the total part of the edge deformed isbetween 10% and 30%.

A shoulder 20 is formed on the edge of the outer bearing race of thebearing 1. A triangular shaped groove 21 is formed in the shoulder 20adjacent the axial face 22 formed with the shoulder. In the presentexample the groove is of the order of 0.3-0.4 mm deep and the clinchinglip 17 is of a similar height. The hole in the retaining plate is madeoversize in relation to the diameter of the shoulder 21.

To secure the retaining plate 6 to the bearing 1 the retaining plate islocated over the bearing with the clinching lip 17 engaging the axialface 22. It may be noted that the fit of the hole 11 over the shoulder20 is loose as indicated by the exaggerated gap shown in FIGS. 3 and 4.An assembly force is then applied in the direction of the arrow in FIG.3 which plastically deforms the clinching lip 17 causing it to engage inthe groove 21 as shown in FIG. 4.

The retaining plate 6 also provides a retaining element in the form of a“U” shaped bracket 23 projecting from an outer periphery of the plate.The Forks of the “U” shaped plate engage a gear change support rod (notshown).

It is undesirable that the plate gauge should be any greater thannecessary in order to minimize the space occupied by the retainingplate. It is essential that the bearing is retained with minimalmovement so that the fastening means need to provide the retaining platewith a clamping action against the axial face of the bearing. It isfurthermore the case that the retaining plate is subject to cyclic axialloads during operation which present a metal fatigue problem.Conventionally punch forming the bosses onto the plate exacerbates themetal fatigue problem by work hardening the plate so that punch formingthe bosses is contraindicated. However, punch forming presentssubstantial economies by comparison with alternative conventionalsolutions to the formation of fastening means. It is a further problemwith punch forming the bosses to ensure that the end faces of the bossesare exactly flat.

In order to enable punch forming of the bosses the plate mayconveniently be formed from a material having a high strain hardeningcoefficient. Preferred examples are austenitic stainless steel grade 304and plain carbon steel grades 1020-1040. An alternative approach is toselect a highly formable material and after formation of the bosses tosubject it to further processes such as surface hardening or theNitrotec process to improve its fatigue tolerance.

FIGS. 7A and 7B illustrate the tooling designed for formation of thebosses. The tooling comprises a die 24 having an arcuate rim 25. Theradius of the arc must be carefully formed to prevent necking in therestraining plate 6. The radius of the arc is preferably formed incompliance with the formula:radius=plate thickness X Awhere “A” has a value between 0.3 and 0.7.

A punch tool 26 is specially shaped to ensure that in cooperation withthe die the end face “F” of the boss 7 is flat and square.

Although the example described uses screws to fasten the plate the useof other fastening means such as rivets is envisaged as within the scopeof the invention.

1-24. (canceled)
 25. A method of forming a boss in a plate to be subjectto cyclic fatigue loads in use comprising, selecting the material of theplate to have a high strain hardening coefficient in excess of 0.35, andpress forming the boss against a die such that the radius of curvatureof the region between the original plate and the wall of the bosscomplies with the formula:radius=plate thickness X A where “A” has a value between 0.3 and 0.7such that the arcuate portion of the boss work hardens under load toproduce a region having a high local tensile strength.
 26. The methodaccording to claim 25 wherein the material of the plate is Austentiticstainless steel grade 304.